Composition and process for cleaning metal

ABSTRACT

A composition for cleaning aluminum and aluminum alloy surfaces which comprises from about 1 to 30 percent by weight phosphoric acid and from about 0.15 to 15 percent by weight nitric acid, the weight ratio of nitric acid to phosphoric acid being about 0.020.6:1. This solution further contains from about 0.05 to 20 percent by weight of a nonionic surface active agent, which is stable in the nitric acid containing solution. This cleaning composition is particularly adapted for use in the spray cleaning of aluminum alloy surfaces which contain 2 percent or more of alloy elements, such as magnesium.

United States Patent Burden et a1.

[ Feb. 29, 1972 [54] COMPOSITION AND PROCESS FOR CLEANING METAL [72] Inventors: Peter Burden, Stoke Poges; Colin Alfred Whitton, Ashford, both of England 21 Appl. No.: 11,331

[30] Foreign Application Priority Data Feb. 17, 1969 Great Britain ..8,489/69 [52] US. Cl ..l34/3, 134/41, 252/79.4, 252/136, 252/142 [51] Int. Cl. ..C23g 1/06, C23g1/12 [58] Field Of Search ..252/79.2, 79.4,101, 136,137, 252/142, 146-151; 134/3, 28, 41

[56] References Cited UNITED STATES PATENTS 2,430,435 11/1947 Sperry ..134/28 X 2,662,814 12/1953 Swihart..... 252/79.4 X 2,867,514 1/1959 Newhard ..134/3 X 3,041,285 6/1962 Newman 1 34/3 X Hoover ..252/79.2 3,448,055 6/1969 Mickclson... 3,457,107 7/1969 Mickclson.. 3,458,354 7/1969 Reich 3,518,118 6/1970 Farison ..l34/3X OTHER PUBLICATIONS Schwartz et al., Surface Active Agents and Detergents, (1958),Pp. 125-127.(A.U. 171) McCutcheon, Detergents and Emulsifiers 1963 Annual, (1963), pp. 4, 100. (A.U. 171) Primary ExaminerMorris O. Wolk Assistant Examiner-D. G. Millman Att0rneyStanley l-l. Lieberstein and William J. Schramm [5 7] ABSTRACT A composition for cleaning aluminum and aluminum alloy surfaces which comprises from about 1 to 30 percent by weight phosphoric acid and from about 0.15 to 15 percent by weight nitric acid, the weight ratio of nitric acid to phosphoric acid being about 002-06: 1. This solution further contains from about 0.05 to 20 percent by weight of a nonionic surface active agent, which is stable in the nitric acid containing solution. This cleaning composition is particularly adapted for use in the spray cleaning of aluminum alloy surfaces which contain 2 percent or more of alloy elements, such as magnesium.

6 Claims, No Drawings COMPOSITION AND IROCESS FOR CLEANING METAL This invention relates to a composition and process for cleaning aluminum and aluminum alloy surfaces and more particularly it relates to an aqueous acidic cleaning composition particularly adapted for the spray cleaning of high-alloy content aluminum alloys.

l-leretofore, it has been proposed to treat the surfaces of aluminum and aluminum alloys with various acidic solutions, for varying purposes. For example, pure or low-alloy aluminum containing at least 98 percent and generally 99 percent or more aluminum, has been brightened by treatment with highly concentrated acid solutions, including acid solutions which contain high concentrations of phosphoric acid and nitric acid. Typically, these solutions are used in hot baths in which the aluminum is immersed and although they effectively brighten pure aluminum and low-alloy aluminum, they have not been generally found to be effective in brightening aluminum alloys of higher alloy content.

In other treatments, aluminum alloys of higher alloy content, particularly in the form of castings, have been deoxidized to make them suitable for subsequent treatments, such as anodizing or chromating. In these processes, various mixtures of mineral acids, frequently including hydrofluoric acid, have been used, the castings often being immersed in the hot acid solutions. It has been found, however, that unless the acid treating solutions contain hydrofluoric acid, an adherent silicone-containing smut remains on the alloy surface. Thus, the use of hydrofluoric acid in these solutions has been necessary, although this acid is both difficult to use and causes problems in the disposal of efiluent.

In still other treatments, aluminum alloys, particularly after extrusion, Frequently, however, this treatment also produces a smut deposit on the aluminum surface, although this deposit contains no appreciable amounts of silicone and is usually removed by treatment with nitric acid.

Although there have been proposed numerous treatments for aluminum alloys surfaces, none of the treatments which have heretofore been used have been completely effective in cleaning the aluminum alloy surfaces, particularly where these surfaces are of a high-alloy content. The need for such a cleaning composition has become more pressing in recent years with the more extensive use of aluminum alloys in the transportation industry, particularly in freight containers and trucks or similar road vehicles. These structures contain surfaces, such as walls, panels, and the like, made of highstrength aluminum alloy sheets, particularly aluminum alloys containing 2 percent or more magnesium, in addition to other alloying elements. When these surfaces are exposed to the atmosphere, they become soiled and tarnished and must be periodically cleaned. The atmospheric attack on these surfaces produces corrosion products to which dirt and other soil stick so firmly that it cannot simply be washed off. in cleaning these surfaces, the cleaning operation must, in general, be carried out at atmospheric temperature. In structures such as freight containers, trucks and the like, the aluminum alloy parts are frequently adjacent to or supported by iron or steel. Accordingly, any cleaning processes which are used must not only be safe for the aluminum surfaces but, additionally, must not cause any damage to other metal surfaces. Up to the present time, the various known cleaning processes have not been completely sa,isfactory for these types of cleaning operations.

It is, therefore, an object of the present invention to provide an improved composition and process for the cleaning of aluminum and aluminum alloy surfaces.

Another object of the present invention is to provide an improved composition and process for cleaning aluminum alloys of high alloy content, particularly as these form a part of freight containers, trucks, and the like.

These and other objects will become apparent to those skilled in the art from the description of the invention which follows.

have been etched with alkaline solutions.

Pursuant to the above objects, the present invention includes a cleaning solution suitable for the spray cleaning of aluminum and aluminum alloy surfaces which comprises an aqueous acidic solution containing from about 1 to 30 percent by weight phosphoric acid, from about 0.15 to 15 percent by weight nitric acid, the weight ratio of nitric acid to phosphoric acid being about 0.02-0.6:1, and from about 0.05 to 20 percent by weight of a nonionic surface active agent which is stable in the acid solution.

More specifically, the compositions of the present invention are aqueous solutions of a mixture of mineral acids and a stable nonionic surface'active agent. The mineral acids in the solution are phosphoric acid, which is desirably present in an amount within the range of about 1 to 30 percent by weight, with amounts within the range of about 3 to 15 percent by weight being preferred, and nitric acid which is present in an amount within the range of about 0.15 to 15 percent by weight. The weight ratio of the nitric acid to phosphoric acid is from about 0.02-0.6: l and preferably is at least 0.04: l

It has been found that the present solution must contain phosphoric acid as this attacks the aluminum surface without dulling it, and further, forms protective coatings on iron and steel which may be adjacent to the aluminum surfaces. Since the cleaned surface is attacked by the phosphoric acid to some extent, thus producing some smut, the nitric acid is necessary in the cleaning composition in order to remove the smut. It has been found, however, that where the nitric acid is present in the above indicated smaller proportions than the phosphoric acid, there is little or no attack by the nitric acid on the iron and steel. It has further been found that the cleaning compositions of the present invention should not contain hydrochloric acid, as this severely attacks iron and steel and, further, should not contain sulfuric acid or hydrofluoric acid as the former dulls the aluminum surface while the latter produces a matte finish on the aluminum and cannot be safely applied in a spray application.

In addition to the phosphoric acid and nitric acid, the cleaning compositions of the present invention also contain a nonionic surface active agent which is stable in the aqueous acid solution. This nonionic surface agent is desirably present in the solution in an amount within the range of about 0.05 to 20 percent by weight of the solution. Although various nonionic surface active agents which are stable and are not destroyed by the nitric acid in the composition may be used, in many instances, the preferred surface active agents are the nonyl phenol-ethylene oxide condensate, particularly those containing from about 6 to 20 ethylene oxide units in the molecule. Of these materials, a particularly preferred surface active agent has been found to be the nonylphenol-ethylene oxide condensate containing about 9 ethylene oxide units.

in addition to the above components, in order to further minimize any attack of the nitric acid on iron and steel, one or more conventional inhibitors may be used in the composition. While any conventional inhibitors may be used, the alkyl substituted thioureas have been found to be extremely satisfactory and of these, di-n-butyl thiourea has been found to be particularly effective. Where such inhibitors are included in the composition they are desirably present in amounts within the range of about 0.001 to 0.02 percent by weight of the solution.

It is to be appreciated, that the particular amounts of the components of the present cleaning compositions may be varied, within the indicated ranges, depending upon the particular cleaning conditions which are encountered in each instance. Thus, the strength of the cleaning solution which is required for effective cleaning in any given period of time will depend to a certain extent upon the extent of the soiling of the surface to be cleaned. Whereas a dirty container or vehicle body which has never been cleaned will require a solution of high-acid concentration and high-surface active agent content, with a vehicle which has been regularly cleaned, e.g., 7

once a week, a much less concentrated solution will be adequate. Thus, within the ranges which have been set forth hereinabove, the specific amounts of the components of the cleaning compositions of the present invention may be varied, depending upon the particular cleaning conditions encountered In this regard, it is to be appreciated that the cleaning solutions may be formulated so that they are ready to use, i.e., they may be made up so as to contain each of the components in the desired amount for the particular cleaning operation. In many instances, however, it may be more convenient to make up concentrate compositions which contain the composition constituents, which concentrates may then be diluted with water as required, to form the desired operating cleaning solutions. Where such concentrate compositions are used, they may desirably contain from about to 40 percent by weight phosphoric acid, with the nitric acid and surface active agent component amounts being increased accordingly so that upon dilution with water, the resulting operating baths will contain the desired amounts of each of these components.

In using the cleaning solutions of the present invention, they I may be applied to the aluminum and aluminum alloy surfaces to be cleaned in any convenient manner. In many instances, it has been found to be particularly preferred if the cleaning solutions are applied to the metal surface to be cleaned by spray application. ln such spraying operations, the solution may be sprayed as such, or may be sprayed as ,a foam, produced by mixing the solution with air. Where the cleaning solution is applied by spraying as a foam, the expansion of the foam, i.e., the ratio of the volume of the foam to the volume of the solution, is typically about 10 to 15, although both greater and lesser expansions may be used, as desired.

In general, it has been found that the cleaning solutions should be retained in contact with the surface to be cleaned for a period of at least about 1 minute, with contact times of from about 2 to minutes being typical, particularly where relatively dilute cleaning solutions are used. Following the application of the cleaning solution, the solutions may then be rinsed off with Water, to provide a clean surface which has been restored, to a great extent to its initial brightness. Additionally, although the cleaning solutions are normally used at ambient temperature, if desired, they may be warmed somewhat to enhance the cleaning effectiveness. Moreover, in order to insure that the solutions have completely covered the surfaces to be cleaned, they may also contain, if desired, an acid-stable dye. Obviously of course, dyes which will stain the aluminum surface or the other metals or painted surfaces used in conjunction with the aluminum will not be used. Where such an acid stable dye is included in the solution, it is very easy to see whether or not the surface is completely covered with the solution and also to determine when the solution has been properly rinsed off of the surface following the cleaning operation.

In order that those skilled in the art may better understand the present invention and the manner in which it may be practiced, the following specific examples are given. in these ex-. amples, unless otherwise indicated, parts and percent are by weight. These examples, however, are not to be taken as a limitation on the present invention but merely as being exemplary thereof.

EXAMPLE l A concentrate composition was formulated containing the following components in the amounts indicated:

. cover the invention broadly in whatever form its principle may This concentrate was diluted with water to form a cleaning solution having a phosphoric acid content of 3 percent by weight. Aluminum freight containers, of an aluminum alloy containing at least 2 percent by weight magnesium, were sprayed with the cleaning solution for 2 minutes, which was rinsed off after a dwell period of 2 minutes. Excellent removal of corrosion product and good brightening of the aluminum alloy surfaces were obtained.

EXAMPLE 2 A concentrate composition was formulated containing the following components in the amounts indicated:

Components Pounds Water 750 Phosphoric acid (l-L P0,) I50 Nitric acid (HNQ Nonyl phenol ethylene oxide containing 9 ethylene oxide units per molecule 20 Di-n-butylthiourea (CJ-L N, S) 0.07

This concentrate was diluted with three times its own weight of water and then sprayed as a foam onto aluminum surfaces of trucks, the expansion of the foam being between 10 and 15. The foam was left in contact with the aluminum surface for 2 minutes and then rinsed off with water. Excellent cleaning and brightening of the aluminum surface were obtained.

EXAMPLE 3 A concentrate composition was formulated containing the This concentrate was diluted with three times its own weight of water and sprayed as a foam, with an expansion of about 10 to l 5, onto a truck body made of aluminum alloy containing at least 2 percent by weight magnesium, using the procedure of Example 2. The period between the spraying and the rinsing with the water in this instance, however, was 8 minutes. Following the water rinsing the surfaces were found to be well cleaned and brightened. Additionally, the surfaces were found to be suitable for painting or lacquering, with the application of a clear lacquer being desirable to retain the brightness of the metal.

While there have been described various embodiments of the invention, the compositions and method described are not intended to be understood as limiting the scope of the invention, as it is realized that changes therewithin are possible and it'is intended that each element recited in any of the following claims is to be understood as referring to all equivalent elements for accomplishing substantially the same results in substantially the same or equivalent manner, it being intended to be utilized.

What is claimed is: v l. A method of cleaning aluminum and aluminum alloy surfaces which comprises spraying the surface to be cleaned with an aqueous acidic solution containing from about 3 to l5 percent by weight of phosphoric acid, from about 0.15 to 15 percent by weight nitric acid, the weight ratio of nitric acid to oxide condensate.

5. The method as claimed in claim 4 wherein the cleaning solution also contains an inhibitor for the attack of the acid solution on iron and steel.

6. The method as claimed in claim 5 in which the inhibitor in the solution is di-n-butylthiourea, which is present in an amount within the range of about 0.001 to 0.02 percent by weight of the solution. 

2. The method as claimed in claim 1 wherein the cleaning solution is sprayed as a foam.
 3. The method as claimed in claim 1 wherein the weight ratio of nitric acid to phosphoric acid in the cleaning solution is at least about 0.04:1.
 4. The method as claimed in claim 3 wherein the surface active agent in the cleaning solution is a nonylphenol-ethylene oxide condensate.
 5. The method as claimed in claim 4 wherein the cleaning solution also contains an inhibitor for the attack of the acid solution on iron and steel.
 6. The method as claimed in claim 5 in which the inhibitor in the solution is di-n-butylthiourea, which is present in an amount within the range of about 0.001 to 0.02 percent by weight of the solution. 